1. Field of the Invention
This invention relates to injector valves and subsurface safety valves and is particularly concerned with an apparatus and method that combines these valves so that they are operated by the same fluid.
2. Description of the Prior Art
Surface controlled subsurface safety valves have been used to control the flow of production fluids from a producing formation to the surface of an oil or gas well. These valves are normally controlled by means of fluid pressure applied from a surface fluid pressure source through a fluid control conduit, such as a small tubing that runs from the fluid source through the wellhead into the annulus between the tubing string and the well casing and to the valve. Water, brine, oil, gas or a similar inexpensive and readily available fluid is normally used to control the safety valve.
An injector valve may be incorporated somewhere in the tubing string of a well so that chemicals can be periodically or continuously injected into the tubing string when the well is producing. Such will be the case when it is desired to inject corrosion inhibitors to prevent or alleviate excess corrosion of the tubing string and the wellhead, or when it is desired to inject a solvent to prevent or alleviate the crystallization and subsequent deposition on the tubing string of paraffins, asphaltenes, sulfur, carbonates, sulfates and similar salts from the well fluids as they are produced through the tubing string. The chemical fluid, like the fluid that controls a subsurface safety valve, is normally supplied to the injector valve from a surface pressure source through a conduit, such as a small tubing that passes from the pressure source through the wellhead into the annular space between the tubing string and the well casing and to the injector valve. When it is desired to inject the chemical fluid, fluid pressure is exerted on the injector valve so that it opens and allows the chemical fluid to flow into the tubing string.
Heretofore, in situations where it was desirable to have both an injector valve and a subsurface safety valve incorporated into the same tubing string, it was necessary to have two separate surface fluid pressure sources--one to control the safety valve and the other to supply the chemical fluid to the injector valve. Each of these fluid pressure sources required its own fluid conduit connecting it to the valve it was operating. Therefore, two separate flange assemblies were required on the wellhead so that the separate fluids could be injected through the wellhead into their individual fluid conduits.
In certain instances the use of two fluid conduits in a well may be impractical because of space limitation. Further, in high pressure gas fields that contain large amounts of corrosive fluids, such as hydrogen sulfide and carbon dioxide, the wellheads are designed to withstand the high gas pressures and are therefore very expensive. Any decrease in the number of flange assemblies required on a wellhead will significantly decrease the cost of the wellhead. Since a well drilled in such high pressure gas fields will produce large amounts of corrosive fluids, the injector valve for injecting corrosion inhibitors into the tubing string cannot be omitted to thereby eliminate its associated flange assembly and fluid conduit. Similarly, the existance of high pressures in such a well dictates the need to control the flow of well fluids and therefore the subsurface safety valve cannot be omitted to thereby eliminate its associated flange assembly and fluid control conduit. It can be seen from the above discussion that in some instances it is desirable to eliminate a second flange assembly and a second fluid conduit from a well and at the same time retain both the injector valve and the subsurface safety valve.